/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 *
 * http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/jsr166e/LongAdder.java?revision=1.14&view=markup
 */

package cn.tang.tframe.monitor.model;

import java.io.Serializable;

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/**
 * One or more variables that together maintain an initially zero {@code long} sum.  When updates
 * (method {@link #add}) are contended across threads, the set of variables may grow dynamically to
 * reduce contention. Method {@link #sum} (or, equivalently, {@link #longValue}) returns the current
 * total combined across the variables maintaining the sum.
 * <p/>
 * <p>This class is usually preferable to {@link java.util.concurrent.atomic.AtomicLong} when multiple threads update a common
 * sum that is used for purposes such as collecting statistics, not for fine-grained synchronization
 * control.  Under low update contention, the two classes have similar characteristics. But under
 * high contention, expected throughput of this class is significantly higher, at the expense of
 * higher space consumption.
 * <p/>
 * <p>This class extends {@link Number}, but does <em>not</em> define methods such as {@code
 * equals}, {@code hashCode} and {@code compareTo} because instances are expected to be mutated, and
 * so are not useful as collection keys.
 * <p/>
 * <p><em>jsr166e note: This class is targeted to be placed in java.util.concurrent.atomic.</em>
 *
 * @author Doug Lea
 * @since 1.8
 */
@SuppressWarnings("all")
class LongAdder extends Striped64 implements Serializable {
	private static final long serialVersionUID = 7249069246863182397L;

	/**
	 * Version of plus for use in retryUpdate
	 */
	final long fn(long v, long x) {
		return v + x;
	}

	/**
	 * Creates a new adder with initial sum of zero.
	 */
	LongAdder() {
	}

	/**
	 * Adds the given value.
	 *
	 * @param x the value to add
	 */
	public void add(long x) {
		Cell[] as;
		long b, v;
		HashCode hc;
		Cell a;
		int n;
		if ((as = cells) != null || !casBase(b = base, b + x)) {
			boolean uncontended = true;
			int h = (hc = threadHashCode.get()).code;
			if (as == null || (n = as.length) < 1 ||
					(a = as[(n - 1) & h]) == null ||
					!(uncontended = a.cas(v = a.value, v + x)))
				retryUpdate(x, hc, uncontended);
		}
	}

	/**
	 * Equivalent to {@code add(1)}.
	 */
	public void increment() {
		add(1L);
	}

	/**
	 * Equivalent to {@code add(-1)}.
	 */
	public void decrement() {
		add(-1L);
	}

	/**
	 * Returns the current sum.  The returned value is <em>NOT</em> an atomic snapshot; invocation
	 * in the absence of concurrent updates returns an accurate result, but concurrent updates that
	 * occur while the sum is being calculated might not be incorporated.
	 *
	 * @return the sum
	 */
	public long sum() {
		long sum = base;
		Cell[] as = cells;
		if (as != null) {
			int n = as.length;
			for (int i = 0; i < n; ++i) {
				Cell a = as[i];
				if (a != null)
					sum += a.value;
			}
		}
		return sum;
	}

	/**
	 * Resets variables maintaining the sum to zero.  This method may be a useful alternative to
	 * creating a new adder, but is only effective if there are no concurrent updates.  Because this
	 * method is intrinsically racy, it should only be used when it is known that no threads are
	 * concurrently updating.
	 */
	public void reset() {
		internalReset(0L);
	}

	/**
	 * Equivalent in effect to {@link #sum} followed by {@link #reset}. This method may apply for
	 * example during quiescent points between multithreaded computations.  If there are updates
	 * concurrent with this method, the returned value is <em>not</em> guaranteed to be the final
	 * value occurring before the reset.
	 *
	 * @return the sum
	 */
	public long sumThenReset() {
		long sum = base;
		Cell[] as = cells;
		base = 0L;
		if (as != null) {
			int n = as.length;
			for (int i = 0; i < n; ++i) {
				Cell a = as[i];
				if (a != null) {
					sum += a.value;
					a.value = 0L;
				}
			}
		}
		return sum;
	}

	/**
	 * Returns the String representation of the {@link #sum}.
	 *
	 * @return the String representation of the {@link #sum}
	 */
	public String toString() {
		return Long.toString(sum());
	}

	/**
	 * Equivalent to {@link #sum}.
	 *
	 * @return the sum
	 */
	public long longValue() {
		return sum();
	}

	/**
	 * Returns the {@link #sum} as an {@code int} after a narrowing primitive conversion.
	 */
	public int intValue() {
		return (int) sum();
	}

	/**
	 * Returns the {@link #sum} as a {@code float} after a widening primitive conversion.
	 */
	public float floatValue() {
		return (float) sum();
	}

	/**
	 * Returns the {@link #sum} as a {@code double} after a widening primitive conversion.
	 */
	public double doubleValue() {
		return (double) sum();
	}

	private void writeObject(java.io.ObjectOutputStream s)
			throws java.io.IOException {
		s.defaultWriteObject();
		s.writeLong(sum());
	}

	private void readObject(java.io.ObjectInputStream s)
			throws java.io.IOException, ClassNotFoundException {
		s.defaultReadObject();
		busy = 0;
		cells = null;
		base = s.readLong();
	}
}
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